1. Field of the Invention
Aspects of the present invention relate to an electrode assembly and a secondary battery having the same, and more particularly, to an electrode assembly and a secondary battery having the same, which improves efficiency and stability thereof.
2. Description of the Related Art
In recent times, various compact and handheld electronic/electrical appliances, such as cellular phones, notebook computers, camcorders, and like devices, have been widely developed and produced. The handheld electronic/electrical appliances include a battery pack installed therein to operate as a driving power source without a separate power source. The built-in battery pack includes at least one battery to output a specific level of voltage for driving the handheld electronic/electrical appliances for a specific time.
A secondary battery is widely used because it is rechargeable and can be manufactured in a compact size and to have high capacity in consideration of practicality and economical efficiency. Among the secondary batteries, a lithium secondary battery is widely used due to an operating voltage (i.e., 3.6V) three times higher and a higher energy density per unit weight than a nickel-cadmium (Ni—Cd) battery and a nickel-metal hydride (Ni-MH) battery, which are widely being used in the handheld electronic/electrical appliances.
Among the lithium secondary batteries, a lithium ion secondary battery includes a bare cell formed by accommodating an electrode assembly having a positive electrode plate, a negative electrode plate, and a separator in a can formed of aluminum or aluminum alloy, sealing the can with a cap assembly, injecting an electrolyte into the can, and sealing the can. A lithium polymer secondary battery having a polymer separator may use a pouch instead of a can because the separator serves as an electrolyte or the separator is impregnated with an electrolytic element, and thus there is less or no leakage of the electrolyte.
An electrode plate is generally formed by applying slurry including an electrode active material on a surface of an electrode collector formed of metal foil. An electrode assembly may include strips of a positive electrode plate, a separator, and a negative electrode plate which are sequentially wound in a jelly-roll type.
An electrode collector has an electrode coating portion formed by applying a slurry long enough to form one electrode, and a non-coating portion, in which an electrode active material is not applied, to which an electrode tab is welded.
A transient phenomenon occurs, in which the slurry is agglomerated, so that a starting region from which the application of the slurry to the electrode collector starts is a little thicker than other regions of the electrode coating portion. Further, a tailing phenomenon occurs, and thus the slurry is applied less at an ending region where the application of the slurry to the electrode collector is terminated than other regions of the electrode coating portion.
The starting and ending regions of the electrode coating portion may damage the separator that electrically insulates the positive electrode plate from the negative electrode plate when pressure supplied in the process of winding the electrode assembly or external pressure is applied thereto. As an internal short circuit between the positive and negative electrode plates is generated at these regions due to the damaged separator, a battery production yield may be decreased and safety concerns may arise.
Accordingly, in the conventional art, insulating layers were formed at the starting and ending regions of the slurry application to prevent these problems. However, in a conventional electrode assembly, since an insulating layer partially covers an electrode coating portion, a reaction area of the electrode coating portion is decreased. Thus, the capacity of the battery is reduced as much as the decreased reaction area. Further, since an insulating layer is formed in the electrode coating portion, a diameter of an electrode assembly which is wound in a jelly-roll type becomes larger. Furthermore, by a reaction of each component at a bonding portion between an electrode coating portion and an insulating layer, dissimilar metals other than cobalt may be released.